Binding of human plasminogen and high-molecular-mass kininogen by cell surface-exposed proteins of Candida parapsilosis

Abstract

Pathogenic microbes can recruit to their cell surface human proteins that are components of important proteolytic cascades involved in coagulation, fibrinolysis and innate immune response. Once located at the bacterial or fungal surface, such deployed proteins might be utilized by pathogens to facilitate invasion and dissemination within the host organism by interfering with functionality of these systems or by exploiting specific activity of the bound enzymes. Aim of the study presented here was to characterize this phenomenon in Candida parapsilosis (Ashford) Langeron et Talice - an important causative agent of systemic fungal infections (candidiases and candidemias) in humans. We have investigated the interactions of fungal surface-exposed proteins with plasminogen (HPG) and high-molecular-mass kininogen (HK) - the crucial components of human fibrinolytic system and proinflammatory/procoagulant contact-activated kinin-forming system, respectively. After confirming ability of the fungal surface-exposed proteins to bind HPG and HK, four of them - two agglutinin-like sequence (Als) proteins CPAR2_404780 and CPAR2_404800, a heat shock protein Ssa2 and a moonlighting protein 6-phosphogluconate dehydrogenase 1 - were purified using ion-exchange chromatography, gel filtration and chromatofocusing. Then, their affinities to HPG and HK were characterized with surface plasmon resonance measurements. The determined dissociation constants for the investigated protein-protein complexes were within a 10 M order for the HPG binding and in a range of 10-10 M for the HK binding. Detailed characterization of adsorption of these two important plasma proteins on the fungal cell surface may help to increase our understanding of molecular mechanisms of C. parapsilosis-dependent candidiasis.

Candida parapsilosis: from Genes to the Bedside

“…Fungal proteins with possible human plasminogen and high-molecular-mass kininogen binding roles were also later identified. These include the heat shock protein Ssa2, the abovementioned Als-like proteins, and 6-phosphogluconate dehydrogenase 1 (217,218). This could represent a mechanism to disguise the fungal cells, avoiding recognition by elements of the immune system.…”

What We Do Not Know about Fungal Cell Adhesion Molecules

“…The GPI anchor is added in the ER, then the glycan is cleaved at the cell surface, and the adhesin becomes crosslinked to cell wall β1, 6 glucan [ 8 , 14 , 39 , 40 ]. Homologs of known GPI-anchored adhesins have been identified in other species, and in a few cases they have been functionally assayed [ 41 , 42 ].…”

Plasminogen-binding proteins as an evasion mechanism of the host’s innate immunity in infectious diseases

“…Fungal parasite species express Plg-binding proteins ( Table 2 ). Candida species have been reported to exhibit numerous Plg-binding proteins: eight proteins have been reported in Candida albicans: phosphoglycerate mutase, alcohol dehydrogenase, thioredoxin peroxidase, catalase, the transcription elongation factor, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase, and fructose bisphosphate aldolase [ 107 ]; four proteins have been reported in C. parapsilosis: CPAR2_404780, CPAR2_404800, Ssa2, and 6-phosphogluconate dehydrogenase 1 [ 108 ]. In the case of Cryptococcus neoformans , 18 proteins have been identified as capable of binding host’s Plg system to allow the fungus to cross tissue barriers, supporting the hypothesis that Plg binding may contribute to trespass the blood–brain barrier [ 109 ].…”